1. Field of the Invention
The present invention relates to a fixing member and an image heat fixing apparatus and an electrophotographic image forming apparatus employing the fixing member.
2. Description of the Related Art
Heretofore, an electrophotographic image forming apparatus, such as a copying machine, a printer, and a facsimile equipment, has been provided with an image heat fixing apparatus in some cases.
Herein, the image heat fixing apparatus is an apparatus which heat-treats a recording material bearing an image with heat and pressure. As such an image heat fixing apparatus, a fixing apparatus which heat-treats an unfixed toner image on a recording material to fix or temporarily fix the toner image is mentioned. Moreover, a gloss increasing apparatus which heat-treats an image fixed on a recording material to increase the gloss of the image, an apparatus which heat-treats a recording material on which an image is formed by ink jet to dry the image, and the like are mentioned.
The image heat fixing apparatus is provided with a fixing member having an elastic layer containing silicone rubber and a thermally conductive filler dispersed in the silicone rubber. As the fixing member, a fixing roller, a fixing film, a pressure roller, and the like are mentioned.
As the thermally conductive filler, although alumina or zinc oxide has been frequently used, all the thermally conductive fillers contain alkali metal ions as impurities.
The fixing member in the image heat fixing apparatus is heated to a high temperature (generally a temperature of about 200° C. to about 250° C.). In such a case, it is known that when alkali metal ions, particularly sodium ions, are present in silicone rubber forming an elastic layer, the heat resistance of the silicone rubber is adversely affected (refer to Japanese Patent Laid-Open No. 2006-336668). Specifically, the hardness of the silicone rubber significantly changes due to cutting of a crosslinked portion of the silicone rubber, reconnection of the cut portions, and the like. In particular, when the addition amount of the thermally conductive filler relative to the silicone rubber in the elastic layer is increased in order to increase the thermal conductivity of the elastic layer, the instability of the hardness of the elastic layer becomes more noticeable.
In order to address the problem, Japanese Patent Laid-Open No. 2006-336668 proposes compounding zinc oxide whose sodium content is small and whose average particle diameter is 1 to 50 μm as the thermally conductive filler.
However, the use of the thermally conductive filler proposed in Japanese Patent Laid-Open No. 2006-336668 has caused a cost increase. Moreover, there has been a problem in that usable thermally conductive fillers have been limited.